In a study of SRS treatment for vertebral metastases in 352 patients with 442 treatments across 7 institutions, long-term pain control was achieved with high rates of complete pain response, with a median follow-up of 11 months. No case of radiation-induced myelopathy was observed, and toxicity associated with SRS was low, with a 10% vertebral fracture rate following treatment.

Shifting the Paradigm for Spinal Metastases with Stereotactic Radiosurgery

John H. Shin, MD, is a neurosurgeon whose scalpel of choice is as likely to be a tightly focused beam of radiation as it is a blade of stainless steel. As director of the multidisciplinary MGH Center for Spine Metastases (a part of the Neurosurgical Spine Service), he oversees the Stereotactic Spine Radiosurgery (SRS) program, in collaboration with specialists in Radiation Oncology. SRS allows the delivery of focused radiation to precise targets within the spinal column for pain relief as well as durable local tumor control. Within spinal oncology, SRS has made an enormous impact on the way patients with metastases are treated. “Radiosurgery has shifted the paradigm of how we treat these patients by allowing us to minimize the morbidity of conventional surgery and to focus on tumor control,” he says.

The differences between SRS and conventional radiotherapy are profound, beginning with the nature of the energy beam directed at the patient, and encompassing treatment duration, potential adverse effects, and patient outcomes. In general, conventional radiotherapy directs a uniform set of radiation beams at a target, with limited ability to focus the beams to conform to the shape of the tumor. The dose administered is often limited by nearby vital organs as well as the patient’s previous radiation history. With conventional radiation, the total dose is often delivered over two weeks or more, to allow damaged cells to heal before being irradiated again. This is done to minimize damage to the skin, spinal cord, and surrounding tissues.

With SRS, high-definition imaging and computer-assisted navigation allow the delivered radiation to be formed to the shape of the tumor and achieve its maximum intensity only within its borders, largely sparing surrounding tissue from the toxic effects of radiation. “The whole point is to maximize radiation dose to the tumor while sparing the spinal cord,” Dr. Shin says. “Spinal cord injury, whether through surgery or radiation, is devastating.” As a consequence of the beam’s tight focus, the dose delivered can be much higher, a benefit for historically radiation-resistant tumors such as renal cell carcinoma. The treatment can also be delivered in one session, typically in less than an hour. This is not only more convenient for the patient, but it minimizes targeting error, since the patient is not repositioned multiple times for multiple treatments.

The challenges of using SRS for spine tumors include conforming the dose to the complex shape of each tumor while minimizing risk to nearby vital organs. In preparation, patients often undergo high-definition MR imaging, with careful attention to the intended target. In patients who have had previous spine stabilization surgery, a CT myelogram is performed to better identify the spinal cord. Dr. Shin then meets with the radiation oncologist and medical physicist to identify the margins of the tumor and to plan the treatment. “We literally draw lines around the structures we want to target,” he says. Once the targets and dose limits are agreed upon, the team will do a “phantom run” to verify the parameters, before treating the patient. Patients are evaluated in multidisciplinary clinic one month after treatment, and then every three months thereafter.

Patient selection is the key to success, Dr. Shin says. “We cast a pretty wide net. SRS can be used as a post-operative adjuvant or as a stand-alone treatment for painful vertebral metastases. It can also be a valuable option for patients previously treated with standard radiotherapy presenting with locally progressive disease. Patients with spinal cord compression or mechanical instability are not eligible for SRS treatment. These patients should be considered for surgery.”

The selection process is aided by the multidisciplinary nature of the MGH Center for Spine Metastases. “Cancer care is often very fragmented,” Dr. Shin says, with limited communication between oncologists, radiation oncologists, and surgeons. “What we strive for is an integrated program where patients are evaluated by specialists in spine oncology surgery, radiation oncology, and nursing during the same visit. This establishes a sense of community with the patient and fosters a team-based approach. This way, we can formulate a comprehensive treatment plan and make recommendations based on the latest innovations in surgery, radiation oncology, and palliative care. As a neurosurgeon who specializes in both complex spinal operations as well as radiosurgery, I can help patients evaluate options from both sides of the fence.”